Pulsed D.C. TIG (tungsten inert gas) welding has already been used to advantage in the welding of a variety of special materials particularly in the welding of thin plates. The basic principle of this welding method is cyclically to vary the current between a background level and a higher pulse level of same polarity. The power sources used for this welding method are provided with means for adjusting the frequency, the duration and the amplitude of the pulses.
Welding power sources of this kind generally include silicon controlled rectifiers (SCR) or are wholly transistorized. Contrary to the SCR power sources the transistorized power source has considerable power losses and therefore have only been used in the welding with low currents.